They blame it on weather because u were caught in the service recovery mode following a snow storm. Between legal rest periods and reprocessing pax on long distance service recovery may take 1-2 days.

But OP does raise a good point, where does one draw a line in blaming the weather after the WX event? Similar on shorter hauls, where does one draw a line in blaming the weather for example if your flying YYC-YVR at 20:00 and the flight was late due to a snowstorm in YYZ at 9am earlier in the day.